1. Field of the Invention
The present invention relates to techniques for forming a three-dimensional microstructure by (i) a CVD process consisting of irradiating a sample surface with a focused ion beam or electron beam while blowing a source gas against the surface, (ii) an etching process consisting of irradiating a sample surface with a focused ion beam, or (iii) another etching process consisting of irradiating a sample surface with a focused ion beam or electron beam while blowing an etchant gas against the surface.
2. Description of Related Art
So-called microstereolithography making use of photopolymerization reactions using a synthetic resin material is known as a technique for creating a three-dimensional microstructure. With this method, however, only structures having sizes on the micrometer order or greater can be fabricated. It is difficult to provide controls on the submicrometer to nanometer order. Furthermore, the usable materials are limited to photocurable resins. In this way, there are many limitations. Meanwhile, there is a lot of demand for submicrometer to nanometer-sized three-dimensional microstructures in the form of knives, drills, and manipulator probes used for processing of microscope specimens, spring coils, probes of probe microscopes, and coils of precision electronic circuits. There is a high expectation for supply of techniques of fabricating them. Furthermore, it is considered that these nanometer micromachines will find wide application, ranging from medicine, through biotechnology, audio devices, IT products, and communications to automobiles. It is expected that they will be put into practical use. Attempts have been made to fabricate three-dimensional structures of arbitrary shapes by a CVD microlithography machine using a focused charged-particle beam. In this connection, non-patent Reference 1 (S. Matsui, T. Kaito, J. Fujita, et al., Three-dimensional nanostructure fabrication by focused-ion-beam chemical vapor deposition, “Journal of Vacuum Society” Technol. B18, 2000, Vol. 3168) introduces a method of fabricating a three-dimensional rotational symmetric structure by gradually varying the signal from a pattern generator. Non-patent Reference 2 (R. A. Lee, P. J. Wolpert, FIB Micromachining and Nano-Structure Fabrication, “International Symposium for Testing and Failure Analysis”, Nov. 14-18, 1999) introduces a method of fabricating a three-dimensional structure by varying the dose of charged particles in step with the gray levels of a bitmap.
It is considered that processing using a focused ion beam fundamentally progresses in proportion to the dose of irradiating charged particles whether the method is etching or deposition. However, with the above-described prior art method, it is difficult to accurately fabricate the required three-dimensional microshape. One cause of this is that the etch rate varies according to variations in the irradiation angle to the sample or variations in the used material. Another cause is redeposition phenomenon. Unlike two-dimensional processing, a finished shape is not always in proportion to the dose. Furthermore, where deposition is used, the irradiated cross-sectional area of a three-dimensional structure varies in the direction of height. Therefore, if the dose is kept constant, the amount of adsorbed gas varies, thus changing the deposition rate. Hence, an accurate three-dimensional shape cannot be formed.